Modification of asphalt

ABSTRACT

A bituminous composition comprising: (a) a bitumen, (b) a block copolymer of at least one conjugated diolefin and at least one vinyl aromatic hydrocarbon, and (c) a thermoplastic or low crystallinity polymer.

BACKGROUND OF THE INVENTION

This invention relates to the modification of asphalt with blockcopolymers of conjugated dienes and vinyl aromatic hydrocarbons andthermoplastic and low crystallinity polymers. More particularly, thepresent invention relates to the modification of asphalt with blends ofsuch block copolymers and thermoplastic polymers such as polypropyleneand ethylene vinyl acetate or blends of hydrogenated block copolymersand low crystallinity polymers such as atactic polypropylene. By lowcrystallinity, we mean polymers with less than 40% crystallinity.

While bitumens alone have a satisfactory flow resistance, in contrast,they have poor flexural properties in the cold and, on the other hand,particularly in the cold, they exhibit low ultimate tensile elongationvalues. The industry has blended various polymers with bitumens toimprove these properties. Thermoplastic polymers such as ethylene vinylacetate have been blended with bitumen. Thermoplastic elastomers such asstyrene-butadiene-styrene block copolymers have also been blended withbitumen. Also, amorphous polymers such as atactic polypropylene havebeen blended with bitumen. These materials improve some of theproperties of the asphalt but other properties need improvement.

Asphalt, or bitumen, is commonly used for roofing materials and forpaving applications. Blends of bitumen and elastomeric block copolymershave excellent elasticity, flexibility and adhesion properties whichrender them especially suitable for use in roofing coatings and pavingapplications such as joint sealants and hot mix asphalt concrete.However, their resistance to flow is not always wholly satisfactory.

Furthermore, in the application of polymer-modified asphalt forrollroofing there is a need for elastomeric products which can be torchapplied without worrying about polymer degradation. This suggests thatpolymer which contain little or no unsaturation be used. Currently,rollroofing products are manufactured with either atactic polypropylene(not elastic) or unhydrogenerated block copolymers (requires carefultorching practices).

Thus, there is a need to find a way to improve the high temperature flowresistance of bitumen compositions without hurting the low temperatureproperties and keeping basically the same elasticity and dispersibilityin the bitumen. This problem can be solved by utilizing the bituminouscomposition of the present invention. Many of the performancedisadvantages which exist for asphalt/atactic polypropylene blendsrelative to asphalt unhydrogenated block copolymer blends are overcomeby using the hydrogenated block copolymer/atactic polypropylene/asphaltblends of the present invention. Furthermore, the hydrogenated blockcopolymer/atactic polypropylene/asphalt blends of the present inventionare easily torched and elastomeric.

SUMMARY OF THE INVENTION

The present invention relates to a bituminous composition whichcomprises a bitumen, which can be asphalt, a block copolymer of at leastone conjugated diolefin and at least one vinyl aromatic hydrocarbon anda thermoplastic or low crystallinity polymer. When the thermoplasticpolymer is used, it is preferred that it be used in an amount about 0.1to 15% of the total composition and that the block copolymer be used inan amount of less than 4% but at least 0.1% of the weight of the totalcomposition. The preferred thermoplastic polymers are polyolefins andethylene vinyl acetate. When a low crystallinity polymer is used, it ispreferred that it be used in an amount from 0.1 to less than 20%w. Thepreferred low crystallinity polymer is atactic polypropylene.

DETAILED DESCRIPTION OF THE INVENTION

The bituminous component in the bituminous-block copolymer compositionsaccording to the present invention may be a naturally occurring bitumenor derived from a mineral oil. Also petroleum derivatives obtained by acracking process and cold tar can be used as the bituminous component aswell as blends of various bituminous materials.

Examples of suitable components include distillation or "straight-runbitumens", precipitation bitumens, e.g. propane bitumens, blown bitumensand mixtures thereof. Other suitable bituminous components includemixtures of one or more of these bitumens with extenders such aspetroleum extracts, e.g. aromatic extracts, distillates or residues.

The block copolymer components of the compositions of the presentinvention are block copolymers of at least one conjugated diene and atleast one monoalkenyl aromatic hydrocarbon. The preferred conjugateddienes are butadiene and isoprene and the preferred monoalkenyl aromatichydrocarbon is styrene. Such elastomeric block copolymers can have ageneral formula A-B-A or (A-B)_(n) X wherein each A block is amonoalkenyl aromatic hydrocarbon polymer block, each B block is aconjugated diolefin polymer block, X is a coupling agent and n is aninteger from 2-30. Such block copolymers may be linear or may have aradial or star configuration as well as being tapered. Block copolymerssuch as these are well known and are described in many patents,including U.S. Pat. Nos. 4,145,298, 4,238,202, Re. 27,145, and U.S. Pat.No. 5,039,755, which describe hydrogenated block copolymers containingbutadiene. These patents are herein incorporated by reference. Thedescription of the type of polymers, the method of manufacturing thepolymers and the method of hydrogenation of the polymers is describedtherein and is applicable to the production of block copolymerscontaining other vinyl aromatic hydrocarbons and other conjugated dienessuch as isoprene or mixtures of conjugated diolefins.

The molecular weights of these block copolymers may vary over a widerange. However, it is preferable that the contour arm molecular weightof the block copolymers range from 30,000 to 300,000. At lower molecularweights, they must be added at high concentrations and at highermolecular weights, they are expensive and give compositions that aredifficult to process. These molecular weights are the peak molecularweights (of the dominant species) determined by gel permeationchromatography.

The molecular weight ranges referred to herein are the contour armmolecular weights. Radial and star polymers have much higher totalmolecular weight than linear polymers do but the mechanical propertiesconsidered herein are dependent not upon the total molecular weight inthe case of radial and star polymers but rather on the molecular weightof the contour arms of those polymers. For a linear A-B-A polymer, thecontour arm molecular weight is the same as the total molecular weightand the molecular weight range of the present invention is 30,000 to300,000 for linear polymers. For three arm radial polymers, one mustmultiply the contour arm molecular weight by 1.5 to obtain the totalmolecular weight. Thus, the total molecular weight range for a three armpolymer of the present invention would be 45,000 to 450,000. For a fourarm radial polymer, the range would be two times the contour molecularweight range or 60,000 to 600,000. In general, for a coupled radial orstar polymer (AB)_(n) X, the contour arm molecular weight is themolecular weight along the contour arm of the molecule, which is (AB)₂.Thus, for a coupled radial or star (AB)_(n) X, the total molecularweight range is (n/2) times the contour arm molecular weight range.

A wide variety of thermoplastic polymers may be used in the blends ofthe present invention. Such polymers include ethylene polymers such asethylene vinyl acetate (EVA), styrenic polymers like styrenebutadienerubber, polyolefins such as polyethylene (PE) and polypropylene (PP),blends of PE/PP, PE/EVA, PP/EVA and PP/PE/EVA, and mixtures of recycledplastics of the above (which may contain other plastics), and thosewhich are described in U.S. Pat. No. 3,978,014 which is hereinincorporated by reference, etc. The preferred thermoplastic polymers tobe used herein are ethylene vinyl acetate and polyethylene (virgin orrecycled) because these products are capable of improving thetemperature performance of asphalt. When the thermoplastic polymer isused in the blend of the present invention, it is preferred that it beused in an amount from 0.1 to 15% of the total bituminous compositionbecause these thermoplastic polymers can improve the high temperatureflow resistance of the bitumen by increasing stiffness and viscositywhile doing little to hurt the low temperature properties andelasticity. If more than 15% is used, the thermoplastic polymer/asphaltblend is unprocessable with conventional equipment. The block copolymerin this situation should be used in an amount less than 4% but at least0.1% of the total bituminous composition because in this range theformation of a polymeric "network", where a continuous portion of blockcopolymer-modified asphalt exists, is possible. We prefer 3 to 4% w.

Low crystallinity polymers having less than 40% crystallinity such asatactic polypropylene, ethylene-propylene copolymers, ethylene-propylenerubber, ethylene-propylene-diene rubber, linear low densitypolyethylene, ultra low density polyethylene and ethylene acrylic andmethacrylic acid copolymers can be used to advantage in the presentinvention. The preferred low crystallinity amorphous polymer is atacticpolypropylene. When these polymers are used, it is preferred that theybe used in an amount from 0.1 to less than 20% by weight and that theblock copolymer be used in amount from 0.1 to 8%w. In general, one wantsto add enough block copolymer so that the blend is elastomeric andenough of both polymers to obtain good flow resistance.

The compositions of the present invention may contain other materialssuch as fillers including calcium carbonate, limestone, chalk, groundrubber tires, etc. If other materials are added, the relative amounts ofthe bitumen and the polymers specified above remain the same.

The bituminous block copolymer compositions of the present invention maybe prepared by various methods. A convenient methods comprises blendingof the components at an elevated temperature, preferably not more thanabout 250° C. to keep the asphalt heating costs down. Other methods forpreparing the composition of the present invention include precipitationor drying of the components from a common solvent and emulsifying thepolymer with an asphalt emulsion.

EXAMPLES

Several different blends of asphalt and polymeric materials were madeand their properties were compared. These blends were simply made byblending the materials together in a laboratory high shear mixer at atemperature of about 200°-220° C.

The materials used include Type III asphalt which is a blown asphaltfrom GAF Corporation. WR AC-10 is an asphalt grade made by Shell OilCompany at its Wood River Refinery. POLYTAC R-500 polymer is an atacticpolypropylene from Crowley Chemical Company. D1101 is KRATON® D1101rubber, a linear styrene-butadiene-styrene unhydrogenated blockcopolymer made by Shell Oil Company having a molecular weight of111,000. The SEBS is a hydrogenated styrene-butadiene-styrene blockcopolymer having a molecular weight of 170,000.

The blends were tested for the various physical properties as describedin the table below:

    __________________________________________________________________________                           30% POLYTAC                                                                            6% SEBS                                               TYPE III                                                                            12% D1101                                                                              R-500    15% POLYTAC R-500                             PROPERTY                                                                              ASPHALT                                                                             88% WR AC-10                                                                           70% WR AC-10                                                                           79% WR AC-10                                  __________________________________________________________________________    Soft. Pt.                                                                             199° F.                                                                      227° F.                                                                         221° F.                                                                         233° F.                                Vertical Flow,                                                                        194° F.                                                                      <194° F.                                                                        203° F.                                                                         221° F.                                Pass                                                                          Tensile Str.                                                                          73 PSI                                                                              133 PSI  28 PSI   136 PSI                                       Tensile Elong.                                                                        11%   1982%    21%      1762%                                         Cold Temp.                                                                             39° F.                                                                      -31° F.                                                                          3° F.                                                                           7° F.                                 Flex, Pass                                                                    Fatigue Life,                                                                         50    >10,000  <1000    >10,000                                       Cycles to Fail                                                                __________________________________________________________________________

The data in the above table show that relative to asphalt/atacticpolypropylene blends, the blends of the present invention, representedby the column at the far right of the table, exhibit improved polymerdispersion in the asphalt, much higher tensile strength and tensileelongation, improved high temperature flow resistance and significantlyincreased fatigue life. The fatigue life and elongation improvement isparticularly noteworthy because it places blends of the presentinvention on a par with asphalt/unhydrogenated styrene-butadiene-styreneblock copolymer blends (second column) and therefore eliminates themajor performance distinction between SBS modified and atacticpolypropylene modified rolled roofing membranes.

Similar experiments were performed using KRATON® G1650 rubber, acommercially available linear hydrogenated styrene-butadiene-styreneblock copolymer (MW 67,000), KRATON® G1651 rubber, a hydrogenatedstyrene-butadiene-styrene block copolymer (MW 181,000) and KRATON® G1654rubber, a hydrogenated styrene-butadiene-styrene block copolymer (MW110,000). The same general improvements were observed when thesepolymers were used in place of the SEBS polymer described above. Similarexperiments were also performed using linear low density (lowcrystallinity) polyethylene and atactic propylene/ethylene copolymers.The same general improvements were observed when these two polymers wereused in place of atactic polypropylene.

Furthermore, blends of the present invention contain only polymer withlow or no main chain unsaturation. These blends can be used to makerollroofing which is both elastomeric and easily torched. "Easilytorched" refers to the ability of a product to not be easily degraded bytorching. Such a product does not require careful torching practices.

We claim:
 1. A bituminous composition comprising:(a) a bitumen, (b) atleast 0.1 but less than 4 wt % of a block copolymer of at least oneconjugated diolefin and at least one vinyl aromatic hydrocarbon, and (c)from 0.1 to 15 wt % of a thermoplastic polymer.
 2. A bituminouscomposition comprising:(a) a bitumen, (b) from 0.1 to 8 wt % of a blockcopolymer of at least one conjugated diolefin and at least one vinylaromatic hydrocarbon, and (c from 0.1 to less than 20 wt % of a lowcrystallinity polymer which contains less than 40% crystallinity.
 3. Thecomposition of claim 2 wherein the low crystallinity polymer is atacticpolypropylene and the block copolymer is a hydrogenatedstyrene-butadiene-styrene block copolymer.